Method of forming non-spherical atomized particles of magnesium and its alloys



y 1960 G. F. HERSHEY ET AL 2,934,787

METHOD OF FORMING NON-SPHERICAL ATOMIZED PARTICLES OF MAGNESIUM AND ITSALLOYS Filed July 5, 1957 INVENTORS.

Gore 017E Hershey Norman R. CO/brf/ BYE (if: 5%

IVIETHOD F FORMING NON-SPHERICAL ATOM- IZED. PSARTICLES 0F MAGNESIUM ANDIT ALLOY Application July 5, 1957, Serial No. 670,143

8 Claims. (Cl. 18-473) This invention relates to improvements in theprocess of atomizing magnesium and its alloys to obtain nonsphericalsolid particles.

One of the objects of the invention is to provide a methodby whichirregularly shaped particles of rather uniform weight are obtained.

A further object is to provide a process in which the irregularity ofshape of the metal particles can be regulated to a certain extent.

Another object is to provide a process of producing irregularly shapedparticles broad enough in principle to be applicable to either disc orjet atomizing methods.

' The method herein referred to as disc atomizing is defined as follows:

Molten metal is allowed to fall freely in a thin stream onto a rapidlyrotating disc in the presence of a nonreactive gas. The molten metal isflung off the disc in fine particles which cool quickly, therebyproducing a fine particulated product.

The method herein referred to as jet atomizing is defined thusly: I

A thin stream of non-reactive gas so that the stream of molten metal isdispersed into minute particles which instantly solidify, therebyproducing particulated metal.

Other objects and advantages of the invention will be apparent duringthe course of the following description.

In US. Patent 2,676,359 there is disclosed a method of atomizing (hereinreferred to as jet atomizing) magnesium and its alloys which involvesthe impingement of acool hydrocarbon gas (methane, ethane, propane,butane), containing an entrained neutral liquid as a fog, against a thinstream of the molten metal. particles of metal thus obtained are jaggedrather than smooth, are capable of being compacted under pressure, andreadily ignite with the flame of a match.

The present invention concerns an improvement of the foregoing method ofatomizing magnesium and its alloys to produce irregularly shaped solidparticles and is based upon the discovery that by adding a controlledsmall amount of elemental oxygen to a non-reactive gas, used either asthe cooling ambient atmosphere in disc atomizing or as the dispersingmeans in jet atomizing, nonspherical particles of a desired irregularityof shape and uniformity of weight are obtained, whereas sphericalparticles are obtained upon using said same non-reactive gas without theaddition of said controlled small amount of elemental oxygen. Thenon-reactive gas may be a hydrocarbon gas or other inactive gas or gasmixtures which allow the formation of spherical particles in thesubstantial absence of oxygen. The invention then consists of the methodherein fully described and particularly pointed out in the claims.

Referring to the accompanying drawings:

Fig. 1 is a view at a magnification of 11 diameters of a circled portionof a sample of atomized magnesium alloy made by disc atomizing with 3.05volume percent oxygen present in the hydrocarbon gas charged to thespace of molten metal is discharged into a jet 7 p atent O F 2,934,787Patented May 3, 1960 2 in which the disc operates, the sample beingspread thinly on a black background. I

Figs. 2, 3, and 4 are each a similar view of a circled portion of athinly spread sample of the same magnesiumbase alloy disc atomized in anatmosphere of hydrocarbon gases containing, respectively, 0.856, 0.650and 0.345 volume percent oxygen.

Fig. 5 is'a similar view of a circled portion of a sample of the samealloy as that of the previous figures similarly disc atomized but withonly 0.19 volume percent of oxygen in the hydrocarbon gas atmosphere asa blank for comparison.

According to an embodiment of the invention, the magnesium ormagnesium-base alloy to be atomized is brought to the molten state. Themolten-metal is allowed to. fall freely in a thin stream onto a rapidlyrotating disc in the presence of anon-reactive gas which contains, inadmixture, .a small amount of elemental oxygen in the concentrationrange of 0.2-4.5 volume percent. Examples of non-reactive gases whichmay be used are hydrocarbon gases such as natural gas and moreparticular those containing from one to four carbon atoms, helium, argonand mixtures thereof.

The upper limit of oxygen concentration permissible in said ambient gasis the concentration which is safely below the explosive limit for thehydrocarbon gas used (approx. 5 volume percent). ,For helium-oxygen orargon-oxygen mixtures safety becomes a function of the reactivity ofmagnesium with oxygen. Unsafe oxygen concentrations are well above theworking range of this invention.

While magnesium is reactive with oxygen at temperatures near its meltingpoint (650 C.), at much lower temperatures (ISO-200 C.) reactivity isdecreased. Further, reactivity of magnesium with low concentrations ofoxygen is less than with low concentrations of water at the temperatureswhich particles assume within a few seconds after the atomizing step.Atomized particles produced by our method are subject to less magnesiumoxide contamination than the product made by the method described in US.Patent 2,676,359 in which water is the preferred fog-forming liquid.

Water vapor at concentrations normally present in natural gas has notbeen found deleterious to the practice of our invention. Indeed, naturalgas which has not been" dried is often employed in the manufacture ofThe solid atomized spherical particles of atomized magnesium. Watervapor, if present during the atomizing step in substantialconcentrations will have these effects: (1) it will contribute togreater irregularity of shape of atomized particles, and (2) it willreact with magnesium particles resulting in undesirable magnesium oxidecontamination of the particles.

In controlling the shape of the atomized particles the level of oxygenconcentration is critical as demonstrated by the following examples inwhich oxygen concentrations below the explosive limits are used. Thefour examples demonstrate the practice of the invention within the rangeof oxygen concentration stated. From these examples and the accompanyingdrawings the influence of oxygen can be plainly seen. As oxygenconcentration in the ambient gas is reduced, a decreasing proportion ofthe desired irregular shaped particles is produced while an increasingproportion of smooth round particles is obtained.

EXAMPLE 1 A magnesium-base alloy having a nominal composition of 3percent aluminum, 1 percent zinc, 0.2 percent (min.) manganese, thebalance being magnesium, was disc atomized in an atmosphere of naturalgas containing 3.05 volume percent oxygen. The particle forms were allirregular shapes and stringers. This product is shown in Fig. l.

EXAMPLE 2 The same magnesium-base alloy described in Example 1 was discatomized in an atmosphere of similar natural gas containing 0.856 volumepercent oxygen. The particles formed were mostly irregular shapes withsome stringers and with 25 to 50' percent near spherical. This productis shown in Fig. 2.

EXAMPLE 3 The same magnesium-base alloy described in Example 1' was discatomized inan atmosphere of similar natural gas-containing 0.650 percentelemental'oxygen. The particles formed were 25' to 50 percent irregularshapes and with 50 to 75 percent near spherical. This product is shownin Fig. 3.

EXAMPLE 4 The same magnesium-base alloy'described' in Example 1 was discatomized in an atmosphere of similar natural gas containing 0.345 volumepercent elemental oxygen. The particles formed were about 95 percentspherical shapes and about 5 percent slightly irregular particles. Thisproduct is shown in Fig. 4.

In contrast to the foregoing examples, the blank below and theaccompanying figures demonstrate that spherical particles are obtainedwhen the oxygen content of the ambient gas is maintained below thestated. range.

Blank The same magnesium-base alloy described in Example 1 was discatomized in the same natural gas atmosphere containing 0.19 volumepercent or less oxygen. The particles formed were substantially allnormal instead-0f irregular spherical shapes. An example of suchparticles is shown in Fig. 5.

While the use of a rotating disc to atomize the rnolten metal ispreferred in carrying out our invention, other suitable atomizing meansmay be employed, for example, jet atomizing. Here the magnesium ormagnesium-base alloy to be atomized is brought to the molten state. Themolten metal is allowed to fall in a thin stream while impinged againstit is a jet of non-reactive gas which contains, in admixture, a smallamount of elemental oxygen in the concentration range 0.2-4.5 volumepercent.

It is to be understood that the forms of our invention herewith shownand describedare to be taken as preferred examples of the same and thatvarious changes in the mode of operation may be resorted to withoutdeparting from the spirit of our invention or the scope of the subjoinedclaims.

We claim: 6

1. In a process of atomizing a metal selected from the group consistingof magnesium and magnesium-based alloys in the presence of anon-reactive gas the improvement comprising incorporating a controlledamount of elemental oxygen in the range of 0.3 to 4.5 volume percent inthe non-reactive gas, thereby producing solid particles having irregularform.

2. In a process of atomizing a metal selected from the group consistingof magnesium and magnesium-based alloys by subjecting a thin stream ofthe molten metal toa jet of nonreactive gas the improvement comprisingincorporating in the gas jet a controlled small amount of elementaloxygen in the range of 0.3 to 4.5 volume percent, thereby productingsolid particles having irregular form.

3. The process as in claim 2 in which the non-reactive gas is naturalgas.

4. Ina process of atomizing a metal selected from the group consistingof magnesium and magnesiurnbased alloys by allowing the molten metal tofall freely in a thin stream onto a rapidly rotating disc in thepresence of a non-reactive gas, the improvement comprising incorporatingin the non-reactive gas atmosphere a controlled small amount ofelemental oxygen in the range 0.3 to 4.5 volume percent, therebyproducing solid particles having irregular form.

5. The process as in claim 4 in which the non-reactive gas atmosphere isnatural gas.

6. The process as in claim 4 in which the non-reactive gas atmosphere isa hydrocarbon gas having 1 to 4 carbon atoms.

7. The process as in claim 4 in which the non-reactive gas atmosphere ishelium.

8. The process as in claim 4 in which the non-reactive gas atmosphere isargon.

References Cited in the file of this patent UNITED STATES PATENTS2,113,280 Olin et a1. Apr. 5, 1938 2,287,029 Dowdell June 23, 19422,371,105 Lepscoe Mar. 6, 1945 2,587,614 Golwynne Mar. 4, 1952 2,699,576Colbry et a1. Jan. 18, 1955 FOREIGN PATENTS- 745,081 Great Britain Feb.22, 1956

1. IN A PROCESS OF ATOMIZING A METAL SELECTED FROM THE GROUP CONSISTINGOF MAGNESIUM AND MAGNESIUM-BASED ALLOYS IN THE PRESENCE OF ANON-REACTIVE GAS THE IMPROVEMENT COMPRISING INCORPORATING A CONTROLLEDAMOUNT OF ELEMENTAL OXYGEN IN THE RANGE OF 0.3 TO 4.5 VOLUME PER-